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Black Silicon Wafers Processed Into Solar Cells In Actual Production Line

Natcore Technology’s black silicon wafers have now been processed into actual working solar cells in a production line, rather than a laboratory setting, for the first time. This has been done by one of the world’s largest photovoltaic manufacturers, which is located in China’s Hunan province.

Five batches of the silicon wafers with a black silicon etch were produced in the trial run. Impressively, the conversion efficiencies of the trial-run solar cells hit 15.7% — a figure that can likely be easily increased as the process is optimized.

The achievement represents an important step towards the commercialization of the technology — showing, quite clearly, that the process can be made to be commercially viable in an actual production line.

The specifics are detailed below:

Five batches of silicon wafers with a black silicon etch — prepared by Natcore’s scientists at their R&D Center in Rochester, NY, under an exclusive license from the National Renewable Energy Laboratory — were supplied to the Chinese company for cell finishing and testing. Two of the batches were used as controls to help interpret results. Of the three test batches, one had a diffusion using phosphorous oxychloride (POCl3) applied by Natcore; the remaining test batches were diffused by the Chinese company. In all cases, the Chinese performed the final steps necessary to turn the wafers into solar cells and to test them.

“We put these cells through the Chinese manufacturer’s process with essentially no modification to the process itself, except for the fact that certain steps were completely removed,” states Dr David Levy, Natcore’s Director of Research & Technology. “And the removal of these steps projects to yield cost savings of as much as 23.5%.”

“We came out with an efficiency of 15.7% on this first trial. The Chinese team said they were very impressed, as we were, with this result. Conventional cells made in a similar industrial process do have efficiencies in the range of 17 to 19%. But considering the results of this first attempt, the Chinese engineers feel that we could easily push our black cell efficiency into the high teens.”

“Cells made from wafers using our POCl3 diffusion outperformed the cells made with the Chinese diffusion, which was a bit of a surprise to us. The open circuit voltages of the black cells were in the ballpark of 0.63 V, very close to results obtained on conventional control cells that were made with a silicon nitride passivation layer. That speaks to the good passivation that can be obtained on our black etch,” Levy continued.

“I can’t overstate the importance of this development,” says Chuck Provini, Natcore’s president and CEO. “It demonstrates that our black silicon process is commercially viable in a real production line. It also shows that our process could be integrated into a production line without fear of contamination by the chemicals that our process uses.”

“This is a huge step toward commercialization. It proves our earlier contention that our technology can easily be retrofitted into existing solar cell production lines and can just as easily be incorporated into a new line. Black silicon seems poised to become an important new approach for the industry.”

After completion, the solar cells were shipped back to Natcore for further testing.

For some background — black silicon wafers are (typically) simply silicon wafers etched with billions of nano-sized holes per square inch. These holes and the silicon walls around them are smaller than the light wavelengths hitting them, and so, as a result, there isn’t all that much reflectivity.

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James Ayre 's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

No sure if anybody is still reading this, but an update for geeks. NREL have confirmed that PvWatts does indeed use a standard formula to compensate for different angles of incidence. Technical paper here (link), section 7, equations 3 and 4. Running this through a spreadsheet (mailed to Zach), it gives these reductions in effective irradiance: 39 degrees, 14%; 45 deg, 29%; 60 deg, 50%. The next update to PvWatts will allow users to specify a generic anti-reflection module, but not specific models.
The simplest indicator might be the correction factor for 60 degrees. Anything better than half power is an improvement.

Bob_Wallace

I’ve read it a couple of times but I’m not sure I grasp.

This panel produces 50% more power when the angle of the light is 60 degrees off “straight on”?

If that is correct, then is it 50% of anything meaningful?

What I’d like to see is a side by side comparison of power produced through a solar day. Some indication of how a 15.7% black silicon cell performs against a normal 15.7% silicon cell. What’s the expected daily gain? Where does black silicon sit in terms of stationary/tracking with regular cell?

Vensonata

Continued improvement of pv efficiency and reduction of manufacturing is good, but once we are below $1 watt (as we are now) the final effect for the consumer is minimal. It is the soft costs of racking, inverters, wires, labour, that triple the bottom line. Surely that is where the low hanging fruit is. I use both fixed and tracking racks. The cost of tracking is considerably more expensive than just adding more fixed panels. Even the season adjusting makes less difference than one might expect. If someone can halve the price of inverters it will have much greater impact.

JamesWimberley

There’s clearly a lag between panel and BOS costs, but there’s nothing sacred about the high level of the latter in US rooftop, Utility farms everywhere, and rooftop in Germany and Australia, get system costs about double that of the modules. In any case, the panel and installation sectors are still largely distinct businesses, in spite of the trend to vertical integration for utility. The efforts to cut costs in either do not compete for resources outside government research funding, which no longer drives bread-and-butter innovation. “All of the above” is the right approach, and it’s the one being followed.

Omega Centauri

Besides, higher efficiency translates into less racking, shorter wire runs and less labour, so it does contribute to the “hard” part of BOS. Soft costs are considered to be non hardware related, such as administrative, paying the salesforce etc.

JamesWimberley

Gains from lower reflectivity, through this or other approaches like nanodots or microgrooves, are not IMHO captured by the standard conversion efficiency metric. This is calculated using a standard source perpendicular to the cell. In operation, light strikes a panel from all angles from 0 to 90, so oblique-angle performance is worth having too. PvWatts takes account of varying angles of incidence, but uses standard derating factors for all panels.

I’ve suggested to NREL that they develop a metric that captures oblique-angle efficiency. Essentially this would be stylised annual output per installed watt, for a S-facing panel at optimum tilt at a reference location, assuming (counterfactually) year-round sunlight, but a real curve of angles of incidence calculated from true paths of the sun. If NREL don’t do it, the researchers and manufacturers chasing this problem should band together and create the metric, even if they are rivals in getting products to market.

Omega Centauri

We would have to end up with multiple metrics. Perhaps two numbers would be most useful. Direct incidence, which would be good for areas of high DSI with two axis trackers, and “diffuse” light, which is some sort of average over all angles. Then depending upon the application and location a weighted sum of these numbers could be used to predict output.

JamesWimberley

Yes. Or you could have a single, dimensionless average derate percentage. It’s more important to get a single, comprehensible number that’s good enough for most purposes than an optimal indicator that nobody can relate to except professional developers. The latter can build their own metrics.

Bob_Wallace

Tracked vs. stationary output numbers?

By measuring output at a few different angles a performance curve could be created and used for stationary output rating.

JamesWimberley

Tracking is a way round oblique-angle losses. Perfect tracking as with a fully steerable dish gets you the nameplate efficiency all the time. Affordable tracking systems like single-axis avoid the derating partially. I still think you first need to establish a number for fixed tilt, which is after all the most common geometry. Then you adjust for tracking as is done today on PvWatts.

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